1. Field of the Invention
The invention relates to a method and apparatus for flushing the inside surface of a pipe in the vicinity of a welded seam where a flushing gas is fed to the pipe with a laminar flow.
2. Description of the Prior Art
Technical installations such as production lines for electronic information carriers require a high degree of protection against impurities so that the reject rate remains low. Even very small particles can lead to production defects. In order to achieve good protection against impurities, the system is acted upon by high purity gas during the entire production. This gas may be, for instance, argon.
Austenitic piping is used, the inside surfaces of which are electro polished, for the supply of high purity gas. The piping is constructed from individual tube sections, elbows, T-sections, and valves which are welded together. In the production of the piping, evaporation residues can get into the pipes in the fabrication of the piping during the welding process and thereby later into the pure gas. In order to prevent this the welding root is protected during the welding in the interior of the pipe against oxidation by flushing with an inert gas, for instance, argon. The inert gases required are relatively expensive.
It has been customary to date to feed in a flushing gas with laminar flow. There, however, the flow velocity of the gas at the weld is reduced by the heat supplied there to such an extent that residues can no longer be flushed away with an economically justifiable volume of flushing gas if the inside diameter of the pipe is larger than about 50 mm. Consequently, evaporation residues of low-melting alloy components are precipitated from the liquid melt bath at the inside wall of the pipe immediately next to the welded seam.